The proposed research project is designed to provide detailed structural and functional information on the biogenesis of a single mRNA of known function, namely the mRNA which codes for silk fibroin in the silkworm Bombyx mori. Specific subfragments containing relatively short sequence elements will be obtained from genomic clones of the silk fibroin genes. Some of these fragments will be subcloned in single-stranded bacteriophage. The various fragments will be used in hybridization assays designed to define the detailed molecular mechanism of fibroin mRNA processing. Questions to be answered include the ordering of splicing reactions with respect to polyadenylation, as well as the eventual identification of nuclear fractions containing splicing activity. The mRNA coding for the small subunit of silk fibroin has been recently isolated, and we will attempt the isolation of genomic clones containing this gene. The gene will be sequenced and its presumed regulatory sequences compared to those of the fibroin gene. Experiments will also be designed to test whether the primary transcription product of this smaller gene undergoes splicing reactions.